As temperatures rose this summer, a particularly disturbing type of violence reached a boiling point in the downtowns and wealthier neighborhoods of American cities like Chicago and Washington, D.C. and, in particular, Philadelphia. The attacks were not like the riots that rocked English cities in early August. The media dubbed them “flash mobs” because the young, predominately black participants often used social media and text messages to coordinate the rapid-fire assaults, muggings, and en masse collective shoplifting sprees, much to the chagrin of the tech-savvy performance artists who coined the term.

Though collective violence is nothing new, the technology used to organize it is, and so is, to a lesser extent, the fact that the victims were walking through wealthier and whiter neighborhoods. One Philadelphia victim ended up in the hospital with broken teeth and his jaw wired shut, and another, a 27-year old arts journalist, was beaten so badly that her leg broke. In Chicago, more than a dozen young men beat a 34-year-old after dragging him off of his scooter on the city’s North Side. And in January in Washington, D.C., months before that city’s typical summer crime spike, a group of young teenagers attacked a random man on a subway platform while several others stood by filming it on their cell phones.

“It’s an unfortunate interface between technology, poverty, and a historical legacy of a culture of violence,” says University of Pennsylvania anthropologist Philippe Bourgois, author of the award-winning book In Search of Respect: Selling Crack in El Barrio. Bourgois now studies the drug economy in North Philadelphia, where he lives. “This is an interesting phenomenon in that it’s broken the boundaries of the de facto apartheid that’s so subtly enforced in the United States, enforced by residents and police.”

But the historical record sets a high bar for novelty. And what sociologists call “moral panic” usually develops around crime when the crime is described as “new,” such as the great Satanism scare of the 1980s that prompted parents nationwide to scrutinize teens for heavy metal records, black clothing, or pentagram necklaces, and that encouraged the most likely wrongful conviction of the West Memphis Three.

A case in point is a familiar moment of anxiety over group violence committed by young black and Latino men: so-called “wilding” that, most infamously, was allegedly behind the 1989 rape and beating of the “Central Park jogger” in New York. News stories at the time described “wilding” as a commonplace underclass pastime that involved assaulting or sexually assaulting strangers.

The fever pitch got so high that one New York City Councilman made the unsubstantiated claim that “thousands of teenagers went on bloody rampages in several boroughs” on Halloween. “They moved spontaneously in packs of 20 or 30 and assaulted people at random.”

The obsession with “wilding” was traced back to a single police official’s statement, and the “pastime” appears to have never really existed. Nonetheless, it fueled the sense of certain guilt that settled over the jogger case. The sentences for the five boys convicted were vacated years later when someone else confessed to the crime.

So caution must be heeded when parsing these “flash mobs,” a term now being used to describe an often dissimilar series of events that range from street assaults perpetrated by groups of a dozen or so youth, to collective shoplifting and, initially, hundreds of mostly non-violent kids hanging out in the middle of the street. We in the news media, after all, have a penchant for reporting events as unprecedented.

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The history of American cities is from many angles a history of violence, from the mobs that tarred and feathered British tax collectors during the Revolutionary era to the rampant early 19th century violence between rival firefighting companies. In 1854, Philadelphia was consolidated into the sprawling city that it is today in large part to coordinate a unified police response to mob violence.

While urban violence has been associated with young black men since the 1960s, for the bulk of American history mob attacks were most often initiated by white mobs, Protestant and Catholic alike, attacking blacks. Or Protestant mobs attacking Catholics, including one Philadelphia attack that included gun and cannon fire. In the South and West, the lynch mob persisted as a form of vigilante justice well into the late 20th century.

“The historical pattern of interracial conflict,” says Eric Schneider, a historian of urban violence at the University of Pennsylvania who has written extensively on street gangs and the drug economy, “was always whites going into black neighborhoods, burning down buildings, and hanging people from street poles.”

In 1863, white New Yorkers staged a murderous rampage through black neighborhoods during the “draft riots,” sparked by wealthy whites paying replacements to fight for them in the “nigger war.” There were the bloody white mobs of East St. Louis in 1917 and Tulsa in 1921.

Most collective assaults on whites by non-whites took place during the ghetto riots of the 20th century, beginning with the Harlem riots of 1935, and again in 1943.

“African-Americans were attacking white property, and white commuters who happened to be on trolleys, buses, and cars in black neighborhoods,” explains Schneider. “In the past, that could obviously not be coordinated. The use of new technology makes hit and run attacks on specific targets much more feasible. In the absence of large scale rioting, it means people can disappear with relative anonymity, relatively quickly.”

The Harlem pattern of violence reemerged in American cities during the riots of 1964-67, culminating in the nights of burning and looting that broke out in the aftermath of Martin Luther King Jr.’s April 1968 assassination (and then, almost like a delayed aftershock, came the 1992 L.A. riots and the beating of white truck driver Reginald Denney). White-owned (and in 1992, Asian) stores were looted and burned to the ground. The majority of those killed and injured were black. Police were hit with Molotov cocktails, and sometimes even with bullets fired by snipers. White passersby were assaulted.

Those riots launched a cottage industry of academic and government inquiry, including the liberal National Advisory Commission on Civil Disorders, dubbed the Kerner Commission for its chairman, Illinois Governor Otto Kerner. The Kerner Report documented the poor housing, terrible policing, and deep-seated poverty of the ghetto. And it zeroed in on housing segregation, declaring that “our nation is moving toward two societies, one black, one white separate and unequal."

The reports, nearly a half-century old, read like today’s newspaper editorials, op-eds and letters to the editor. Once again, the debate centers on not only what the violence means, but whether it means anything at all. The difference being that then, at liberalism’s zenith, elites by and large strove to understand ghetto grievances. By 1992, things had changed: New Democrat Bill Clinton, though critical of President George Bush’s neglect and calling for a boost in the minimum wage, had dispensed with New Deal rhetoric and joined Bush in preaching personal responsibility and ‘micro-enterprise zones’ to heal inner-city Los Angeles.

Suburbanization had remade the metropolis into racially distinct urban and suburban polities, undermining much of whatever white commitment to black and brown social welfare existed. As President Ronald Reagan’s historic cut to cities (the federal share of L.A.’s budget fell from 18 percent in 1977 to 2 percent in 1985) drove the Welfare State and Great Society to the margins, an engorged criminal justice system was the only policy tool left at hand.

Though the cause and prevention of riots were analyzed, solutions were not implemented. They were a lesser concern as long as the violence didn’t reach white neighborhoods. Throughout the post-war era, police were always quick to cordon off the ghetto. Today's so-called “flash mobs” are not riots. But they are a form of black collective violence that has broken the cordon. “Despite frequent reports of mayhem in the ghetto, the crimes that most upset the city's collective conscience might be called ‘racial crossover’ crimes, in which a white person is the victim of a black perpetrator,” Yale University sociologist Elijah Anderson wrote in the Philadelphia Daily News. “The victim, a white person who was minding his or her own business, is regarded as particularly undeserving of this fate.”

What’s small in terms of bloodshed is big news when it hits downtown. The flash mobs, unlike riots, go beyond targeting symbols of white society in the ghetto. The mobs emerge downtown. Though parts of Center City Philadelphia are mixing grounds—like the diverse and bustling Reading Terminal Market, or Rittenhouse Square, a venue for both stroller-pushing young professionals and break dancers—the flash mobs put excluded young people briefly in charge of an area that profoundly does not belong to them.

Earlier flash mobs took place during the summer of 2010, when hundreds of young people spontaneously appeared on South Street, a central drag of stores and bars, or outside a movie theater near the University of Pennsylvania. A few kids assaulted bystanders, some quite severely, but most just came to hang out or talk with members of the opposite sex.

The front page of The New York Times national section featured a large photo of just that: hundreds of young black people, standing in the middle of the street, not doing much of anything save for checking their cell phones.

“One needs to have that level of awareness to understand why it’s so exciting for kids,” says Bourgois. “It’s just amazing how unfamiliar the kids on our block are with downtown. It’s extraordinary how much they’re stuck in these little worlds.”

“What happens here is that a small fraction of the violence associated with the neighborhood, the places inhabited by the urban underclass, is being brought into the central city where it disturbs the routine of the upper class and tourists,” says Roger Lane, a historian of violence at Haverford College.

Violence can also spring from boredom, a lack of much else to do, the same way that illicit economies grow among the jobless.

“It has a whole terminology around it, like ‘catching a body.’ It’s a coming of age thing in certain neighborhoods. Or ‘wreck chasing,’” says Bourgois. “In the past this has always been in the neighborhood. It’s kids getting violent on the main street of their neighborhood, the five to 10 blocks their universe usually stays in. What we’re seeing with flash mobs is technology changing this.”

Looting has often accompanied the post-war riot, and conspicuous illegal consumption was a central feature of this summer’s “flash mobs.” In a society where success is defined by get-get-get, the have-nots took.

“Listen man, this is the only time in my life I’ve got a chance to get these things,” a woman carting off a pile of stolen clothing told Philadelphia NAACP President Cecil B. Moore, who was urging calm—in 1963.

In July of this year, 40 youth walked en masse off the elevated train in the working class Philadelphia suburb of Upper Darby and into a Sears, brazenly stealing thousands of dollars in merchandise. Then they walked out. The same thing happened at a boutique in the ritzy Washington, D.C. neighborhood of Georgetown.

During one of the assaults in Center City Philadelphia, a group of young people robbed and assaulted a 25-year-old law student in town from New York to visit his girlfriend. One youth shouted, “iPhone, iPhone!” before the group beat a man to the ground and grabbed at his pockets.

"Wallet! Wallet!" another screamed, as the punching and kicking continued.

This group called themselves the “Young Money Gang.” By all accounts, they had little money, but their youngest member was 11 years-old.

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The fact that this form of violence is happening now does not surprise Bourgois: increasingly inexpensive new technology is in the hands of young people who are living on the short end of rising economic inequality, at the same time as deep cuts to social services, including schools, are being implemented in cities and states across the country (here, here and here).

“There’s a tipping point at some point,” says Bourgois, “where kids just get too bored, and fashions develop around the conjunction of violence and new technology that’s available to young people, new levels of poverty, and lower levels of services going to youth.”

There is, however, no historical correlation between absolute violence and economic hardship. Indeed, violent crime in American cities continues to plummet, as it has since the early 1990s.

“There’s very little correlation between economic conditions and violent crime,” says Schneider, noting the rock bottom crime rates during the Great Depression. “It’s inequality more than economic distress. It’s unequal societies that have very high crime rates. So it’s not surprising that both in the U.S. and U.K., where you see rising levels of wealth disparity, you might see some response to that.”

The riots in the 1960s surprised the liberal establishment because blacks had just experienced two decades of significant social and economic progress. And in the South, nonviolence was winning major legal, political, and social victories. But the progress had alleviated just a small portion of the grievances. Amid rising political consciousness, expectations had never been higher.

With Barack Obama in the White House today, expectations are high once again: in 2009, Pew found that the percentage of blacks who thought African-Americans were better off than five years before nearly doubled between 2007 and 2009. According to Pew, “Barack Obama's election as the nation's first black president appears to be the spur for this sharp rise in optimism among African Americans.”

Yet black experience in this same period of time has been an incomparable disaster: according to a new Pew study, black household wealth fell by 55 percent and Hispanics lost 66 percent during the recession, while whites lost just 16 percent. The average white now has a net worth 20 times larger than blacks and 18 times larger than Hispanics, the largest racial wealth gap in at least a quarter century.

Philadelphia, Chicago, and Washington, D.C., the three cities where the so-called “flash mobs” have been most prevalent, have undergone major downtown renaissances over the past two decades, but the spreading gentrification has failed to deliver economic benefits to poorer neighborhoods.

So why aren’t Americans rioting like the British? Bourgois posits it’s because “we’re not a politicized country, we don’t have that class consciousness.” Rioting does require a degree of political awareness. In 1971, sociologist Jeffrey Paige found that Newark rioters had on average more political knowledge than their non-rioting counterparts and a lot less trust in government than civil rights protesters.

Nonetheless, says Schneider, riots could happen here. The historical conditions seem to be in place.

“I think that we could very easily have the equivalent of the London riots in Philadelphia. All it takes is a hot summer night, a police officer pulling somebody over, or somebody getting shot. That’s what happened in the past in Philadelphia and could easily happen again. The new ingredient in this is use of social media to get people to congregate in a specific place and specific time.”

The response in Philadelphia has been a curfew in Center City and rec centers open late in the neighborhoods. Meanwhile, “flash mobs” invoke what Anderson calls the “iconic ghetto” and the specter of black violence, prompting chidings from middle and upper-class blacks, including Philadelphia Mayor Michael Nutter, that today’s youth are a disgrace to their race. That it is inarguably true that black criminality negatively affects the image of blacks overall, while a miscreant white is a symbol of merely individual sin, indicates just how nettlesome the deeper problems are.

“The fundamental problem is beyond the mayor of Philadelphia,” says Lane. “It’s a huge and decades-long and, I fear, accelerating problem of social inequality and joblessness that in particular affects young black men.”